The invention relates to a fire extinguishing device of the kind which comprises at least one liquid conduit, and which at one end is connected to a source with a fire extinguishing liquid under pressure, and at the other end with channels in a nozzle head with a number of nozzles.
It is a well-known fact that water in its plain state is not a very effective means for extinguishing a fire as up to 98% of the water will not take part mi the extinguishing but in stead slide off the burning objects without ever reaching the primary combustion. If fire has broken out in particularly flammable liquids, such as gasoline, spraying with plain water can on the contrary result in a spreading of the fire.
The water is better utilized when it is carried in the form of small drops. An optimum utilisation is only obtained with finely atomized water which has a very large total surface and evaporates immediately when it is sprayed into areas where a combustion is taking place at a high temperature. The last-mentioned effect is extremely desirable as the smoke gases from the fire are cooled momentarily just as the violent vapour formation also displaces the combustible gases and reduces the oxygen content of the air.
During a fire, air will flow to the primary combustion zone where the oxygen content of the air will feed the combustion. As fine water drops are so small and have a mass so small that they will tend to drift in the air, they can be taken into the combustion zone where the combustion thereby is impeded or stopped altogether. Finely atomized water will also be able to penetrate fibrous material and thereby advantageously be able to reduce its combustibility while small drops merely will remain on the surface of the material.
In a cloud of finely atomized water, the drops will furthermore be so small and have a mutual distance so large that the electric conductivity of the cloud will be very small.
Finely atomized water can therefore be utilized with minimal risk for the operator even if there are live wires at the scene of the fire.
Conventionally, pressures as high as between 150 and 250 bar have been utilized in order to atomize water finely enough for the fighting of a fire. These high pressures require heavy equipment which normally only can be established in stationary and/or large units. Such heavy equipment cannot or only with difficulty be utilized for offensive fire fighting, and the resultant finely atomized water that is formed has furthermore turned out to have a range too short to be able to adequately prevent the fire fighters being injured by the heat sent out by the fire.
For quick and effective extinguishing of fluid fires (e.g., a class B fire) and securing against reignition, it can be necessary to utilize foam which forms a stable carpet of small bubbles for effectively cooling and smothering fires that are difficult to control in any other way.
At fire turn-outs, it will not always immediately be clear if the fire in question is a class A, B, C, or E fire. This means that it, at the time of the turn-out, can be uncertain whether it is one type of fire extinguishing equipment or the other that would be most effective in the given situation, and that therefore should be brought along. It is therefore an advantage if both finely atomized water and foam can be discharged from the same fire extinguishing device so that the choice between foam or finely atomized water as fire extinguishing means only need being made when the fire brigade has arrived at the scene of the fire.
It is furthermore an advantage if the quantity of fire extinguishing means necessary for extinguishing a fire is as small as possible so that the fire extinguishing device is not restricted to stationary use but can also be utilized offensively.
A combined fire extinguishing device is among others disclosed in U.S. Pat. No. 2,832,242. This device can, with a valve, be converted to discharge either atomized water or foam but from the same nozzle type. A nozzle for foam can however not be utilized for finely atomizing of water. The drops in the atomized water, which the conventional fire extinguishing device is able to discharge, will therefore be too coarse to optimally be able to fight a fire.
U.S. Pat. No. 4,420,047 discloses a similar fire extinguishing device for fitting in aircraft. The device can selectively discharge either foam or atomized water but also in this case, from the same nozzle type. This device also does not provide finely atomized water.
Thus, there remains a need for improved fire fighting devices that can provide finely atomized water as well as the versatility to be used for fighting a variety of fires.
The present invention provides a fire extinguishing device of the kind mentioned in the opening paragraph wherewith class A, B, C, and E fires can optimally be fought, that with one single handle can be converted to fighting fires either with foam or water, and that is able to finely atomize water by means of a relatively slight pressure of about 10 to 25 bar. The device can also discharge the finely atomized water with an increased horizontal range of over 10 meters.
According to the invention, this is achieved by the fact that the channels of the nozzle head comprise a first channel connected to an atomizing nozzle for discharging liquid in atomized form, and a second channel which has an air intake and downstream of which is connected to a foam nozzle for discharging liquid in foamed form.
In a preferred embodiment of the invention, the liquid conduit of the fire extinguishing device can have a first branch connected to the first channel of the nozzle head, and a second branch connected to the second channel of the nozzle head. This construction is especially simple to manufacture.
At the branch point, there can furthermore be placed a reversing valve for selectively closing the first or the second channel completely or partly so that there, with a single handle, easily and quickly can be changed between discharging of foam and discharging of finely atomized water.
Operation of the fire extinguishing device is facilitated when a flow gun is inserted into the liquid conduit wherein the flow gun has a gun valve for turning the liquid on and off respectively.
In each of the atomizing nozzles of the fire extinguishing device, there can, at a distance from the nozzle opening, advantageously be placed a partition wall extending transversely to the inner side of the nozzle and together with this defining a nozzle chamber. In the partition wall, a central opening and at least one side opening can furthermore be made. When the fire extinguishing device is utilized for fire fighting with atomized water, a finely atomized water cone is then discharged via the nozzle opening, which water cone is filled in with larger water drops for carrying the finely atomized water with it and thereby increase the range of this considerably.
A number of atomizing nozzles can advantageously be placed at a mutual distance along a circle in the end cover of the nozzle head whereby the device is enabled to discharge a relatively large quantity of atomized water in a joint bundle.
When the central openings of the atomizing nozzles furthermore are arranged with different sizes, a bundle of atomized water with degrees of atomization that advantageously cover a broad spectrum is obtained.
By placing the foam nozzle at or near the centre of the circle along which the atomizing nozzles are placed, it is obtained that foam and atomized water are discharged along the same axis so that the operator easily can change between the two extinguishing means without directly having to alter the axial orientation of the nozzle head.